1. Field of the Invention
The present invention relates to a semiconductor photodetector, and more particularly to a semiconductor photodetector whose upper surface insulating films have the desired thicknesses, and which therefore is adapted to receive and utilize incident light on its upper surface. The invention also relates to a method for manufacturing such a semiconductor photodetector.
2. Background Art
A semiconductor photodetector converts received optical energy into electrical energy and passes the resulting electrical signal to an external device. Its upper surface is covered with insulating films, except for the portion on and in contact with which the upper electrode lies. An important property that such insulating films must have is low reflectivity to the light incident to the photodetector.
Further, in the case of a photodetector of the type adapted to receive and utilize incident light on its upper surface, the upper metal electrode is preferably plated with a metal coating to provide sufficient resistance to external force applied to the electrode due to wiring bonding, etc. Such plating requires that the semiconductor process form a power supply layer on the upper surface insulating films. This power supply layer usually has a structure that includes a Ti layer and an Au layer formed on the Ti layer. The Ti layer underlying the Au layer enhances the adhesion to the insulating films. It should be noted that after the above plating, the unwanted portions of the power supply layer are removed.
Prior art includes JP-A Nos. 5-275549 and 5-218212.
However, such semiconductor photodetectors (having their upper electrode plated with a metal coating by the above plating process) suffer the following disadvantage. Treatment with an HF based chemical solution is required to remove the Ti layer making up the power supplying layer after the plating process. This means that the insulating films under the power supply layer may undergo a reduction in thickness due to such treatment. It should be noted that etching a metal (not necessarily limited to Ti) formed on an insulating film generally reduces the thickness of the film to some degree. This may prevent the insulating film from functioning as a low reflecting coating having the desired low reflectivity.